The invention relates to a tangential-belt drive for an open-end spinning machine of the type having a tangential belt driving the spinning rotor shafts of several spinning units arranged next to one another. The spinning units each include a pressure roller which presses the tangential belt by means of an elastic pressure force against the respective spinning rotor shaft. A rotor brake is provided at each spinning unit which can be actuated by means of an actuating mechanism in such a manner that the pressure roller is lifted off the tangential belt during braking.
A tangential-belt drive of the initially mentioned type is known, for example, from the German Patent Document DE-A 36 13 843. As known also from the German Patent Document DE-A 28 03 052, the actuating mechanism is operated by a piecing carriage which can be moved along the machine and can be applied to the individual spinning units. By way of the piecing carriage, the actuating mechanism is operated such that the spinning rotor shaft is braked before the piecing operation so that then the piecing will take place while the spinning rotor is accelerated again to its rotational operating speed by means of the tangential belt which continues to move at an unreduced speed. In this case, the pressure force of the pressure roller provides that the run-up time from the stoppage to the rotational operating speed will not be too long also in the case of extremely high rotational speeds of the rotor which nowadays may clearly be above 100,000 min.sup.-1 (100,000 revolution per minute).
On the basis of the German Patent Document DE-A 34 01 315, a belt drive for spinning rotors is also known in which the slip is reduced during the piecing operation so that the time period can be reduced which the spinning rotor requires for the run-up from stoppage to its rotational operating speed.
It is an object of the invention to develop a tangential-belt drive of the initially mentioned type such that the consumption of energy may be reduced.
This object is achieved in that the actuating mechanism comprises an actuating lever which is connected with the pressure roller in such a manner that, if it is operated when the brake is released, the pressure roller can be pressed against the tangential belt by means of a supplementary force which increases the pressure force.
In this case, the invention is based on the recognition that nowadays the elastic pressure force is frequently higher than is actually necessary. For the normal spinning operation, a relatively low pressure force is sufficient in order to ensure a secure driving of the spinning rotors at which the given rotational speed is maintained. However, in order to exclude a higher slip during the piecing and during the run-up phase utilized in this case, a much higher pressure force must be provided. This higher driving force which is not required during the normal operation, however, has the effect that deformations of the tangential belt may be caused in the area of the spinning rotor shafts which are connected with an increased power consumption. By means of the invention, it is now possible to make the required higher pressure force available only during the piecing while, in the normal operation, the lower pressure force is sufficient which will then cause a smaller deformation o the tangential belt so that the power consumption can be reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.